Temperature-Controlled Dielectric Characterization of Liquid Crystal at 3.5 GHz based on Cavity Perturbation Method

Accurate temperature-dependent dielectric data of liquid crystal (LC) materials in the sub-6 GHz range are essential for the reliable design of reconfigurable RF components, yet available data are often limited to room temperature, different frequency ranges, or both. To address this gap, this paper presents the temperature-controlled dielectric characterization of an LC material at 3.5 GHz using a resonant measurement method, specifically a rectangular hollow waveguide resonator. The characterized LC is contained in a quartz tube, and temperature control is achieved through a dedicated cooling and heating system, enabling measurements between −50 °C and 120 °C. The dielectric properties are extracted based on cavity perturbation theory. To validate the measurement setup, 1-Butanol is characterized and compared with literature data. The LC mixture GT7-29001 exhibits an anisotropic relative permittivity with values of 3.65 and 2.60 for the parallel and orthogonal orientations, respectively, at 20 °C. The loss tangent is 0.0097 and 0.0264 in the respective orientations. An uncertainty analysis quantifies errors from resonance frequency determination, quality factor extraction, and temperature stability. These results provide design-relevant material data and a validated measurement workflow towards LC-based sub-6 GHz components operating in a wide temperature range.